For high density integration of an optical integrated circuit, stacked waveguides and active interconnection between the waveguides must be attained. In this paper, two thin film slab waveguides stacked on a substrate were used to form a two-story structure. Grating couplers were formed in the waveguides to couple the two waveguides. The coupling equations were derived from mode coupling theory in order to clarify the co-directional and contra-directional coupling characteristics. In co-directional coupling, the wavelength selectivity is small, and high coupling efficiency cannot be expected (less than 25%) if a conventional uniform grating coupler is used. On the other hand, in contra-directional coupling, the wavelength selectivity is high, and high coupling efficiency can be expected if a long grating length and large coupling coefficient can be attained. A contra-directional coupling device with a coupling wavelength of 800 nm was designed and fabricated, and its wavelength dependence was evaluated by using the TE mode. The experimental half-value width was 0.3 nm, which is close to the calculated value of 0.2 nm, indicating that the coupler has a sharp wavelength selective coupling characteristic.